This invention relates to an adhesive composite for use where high moisture vapor transmission is desirable. This invention particularly relates to an adhesive composite for use as a medical dressing.
U.S. Pat. No. 4,112,177 to Salditt et al. discloses a microporous medical pressure-sensitive adhesive tape-construction providing a plurality of layers of pressure-sensitive adhesive wherein the total adhesive mass is microporous. As disclosed at column 4, lines 5-9, the firm underlying layer preserves the porous nature of the adhesive mass and the xe2x80x9cquickstickxe2x80x9d softer outer layer of adhesive adheres very readily to the skin.
U.S. Pat. No. 4,499,896 to Heinecke discloses a wound dressing for wounds having a significant amount of exudate comprising a conformable, moisture vapor permeable, liquid water-impermeable first layer containing at least one hole therein through which exudate can pass, and an imperforate, conformable, liquid water-impermeable, moisture vapor-permeable second layer attached to the first layer and overlaying the hole or holes in the first layer. These layers form a reservoir into which the wound exudate can pass and from which the exudate can evaporate.
European Patent No. 0 257 133 to Ewell discloses a wound dressing containing a fabric layer within which is deposited a layer of a hydrophilic material. Pressure-sensitive adhesive is applied to both faces of the fabric layer. One of the pressure-sensitive adhesive layers is for adhering the dressing onto the patient. A cover layer may be additionally applied to the other pressure-sensitive adhesive layer. The layer of hydrophilic material disposed within the fabric layer is provided to absorb excess exudate from the wound.
U.S. Pat. No. 4,773,409 to Cilento et al. discloses an occlusive wound dressing which includes a flexible closed cell polyurethane foam layer having a pressure-sensitive microporous adhesive applied onto one surface of the foam. A polymeric film may be laminated to the opposite surface of the foam to protect the dressing. The foam itself contains water dispersible, water swellable and/or water absorbing agents.
U.S. Pat. No. 3,800,792 to McKnight et al. discloses a surgical dressing for treatment, particularly of burn wounds, comprising a thick layer of collagen compressed foam film which has been laminated to a thin continuous layer of an inert polymer material such as polyurethane.
U.S. Pat. No. 3,849,238 to Gould et al. discloses an artificial skin comprising a water containing hydrophilic polymer sponge layer and a thinner non-hydrophilic polymer layer which is moisture vapor permeable and gas permeable.
Wound dressings, such as foam and pouch dressings described above, that act as a reservoir for excess exudate perform a specific role in wound therapy, but are not appropriate for all wounds. These wound dressings can be disadvantageous when applied to moderately exudating wounds because, due to their capability of containing fluids, a need for changing these dressings may not be perceived by the user. Because all exudate will be contained by these dressings, they can provide an excessively wet environment for the wound which promotes the growth of bacteria. A reservoir type dressing has a limited useful lifetime on a wound because it eventually will become saturated and must be changed.
As a general rule, as the moisture vapor transmission properties of a film backing or an adhesive are improved, a sacrifice is made in another property. In the case of film backings, an increase in moisture vapor transmission will generally result in a backing with reduced tensile strength and elongation properties. A higher moisture vapor transmissive backing is also typically very sensitive to direct contact with aqueous fluids, which will result in unacceptable swelling of the film so that it no longer stays in place on the substrate. The film may also experience a dramatic loss in tensile strength when exposed to direct aqueous fluid contact.
Similarly, a highly moisture vapor transmissive adhesive will typically display shortcomings in properties such as internal cohesion, which results in residue being left on the skin after removal of the bandage, and an undesirably low level of initial and final adhesion to skin levels.
Transparent dressings currently available on the market utilizing Hytrel(trademark) or Estane(trademark) backings do a generally good job of protecting wounds while permitting some moisture vapor to escape from the site, but could be substantially improved with an increase in moisture vapor transmission if other strength, swell and adhesive properties were not sacrificed.
The present invention provides an adhesive composite having very high moisture vapor transmission properties with no sacrifice of other desirable properties of a wound dressing. This achievement is accomplished by providing a dressing with one or more backing or adhesive layers having the desired moisture vapor transmission properties and additionally providing a supplemental layer of a corresponding backing or adhesive in a thinner thickness than would be required alone, resulting in a dressing having the desired overall properties of a wound dressing.
Specifically, an adhesive composite is provided comprising a polymeric backing layer, a high moisture transmission layer, and a skin contacting adhesive layer. The high moisture transmission layer exhibits certain minimum moisture vapor transmission properties and is selected from a polymeric backing material and an adhesive material, or a combination thereof. When the high moisture vapor transmission layer is a polymeric backing material, the material has a moisture vapor transmission of at least about 2000 g/m2/24 hrs/37xc2x0 C./100-20% RH when one mil thick as tested using the Upright Cup method described in detail herein. When the high moisture transmission layer is a polymeric backing material, the polymeric backing layer has a tensile strength when wet that is no more than 30% less than the tensile strength of the backing when dry. When the high moisture transmission layer is an adhesive material, this material is selected from adhesives having a Standardized Transmission Rate as defined herein of at least about 900 g/m2/24 hrs/37xc2x0 C./100-20% RH. In either case, the material of the polymeric backing layer or the skin contacting adhesive layer is not the same as the material of the high moisture vapor transmission layer. The overall adhesive composite exhibits a moisture vapor transmission rate of at least about 1200 g/m2/24 hrs/37xc2x0 C./100-20% RH. Preferably the overall adhesive composite exhibits a moisture vapor transmission rate greater than about 1500 g/m2/24 hrs/37xc2x0 C./100-20% RH, more preferably greater than about 2000 g/m2/24 hrs/37xc2x0 C./100-20% RH and most preferably greater than about 2500 g/m2/24 hrs/37xc2x0 C./100-20% RH.
The skin contacting adhesive layer is selected from an adhesive material having an initial adhesion to skin peel strength of at least about 15 g/inch (5.9 g/cm).
It is thus envisioned that the adhesive composite structure will comprise at least three layers. Additional layers may be added as desired. For example, when the high moisture transmission layer is a backing material, it may be desirable to xe2x80x9csandwichxe2x80x9d this layer between two polymeric backing layers to protect this layer from contact with liquid moisture.
It has surprisingly been discovered that the disclosed adhesive composite structure exhibits a surprisingly high moisture vapor transmission rate, while at the same time affording excellent strength, swell and adhesive properties.